OBJECTIVE To determine the role of pituitary-level regulation of LH secretion in the neuroendocrine mechanisms mediating social suppression of ovulation in subordinate female marmosets. RESULTS The purpose of the present study was to begin exploring pituitary-level neuroendocrine mechanisms underlying socially-modulated fertility in this primate. Experiment 1 simultaneously measured GnRH (via PPP) and plasma luteinizing hormone (LH, via indwelling jugular catheter) in non-subordinate ovariectomized (OVX) females (n=5) every 10min for up to 12hrs. Although GnRH (1.12 pulse/hr + 0.09) and LH (0.96 pulse/hr + 0.09) pulse frequencies were similar (p=0.4), pulse peaks were not temporally concordant. In Experiment 2, non-subordinate OVX females (n=3) each received 2 intravenous GnRH challenges (200ng, 25g) while plasma LH was sampled every 5min. The latency of peak LH response to GnRH stimulation was delayed by 29.2min + 3.5. Overall, these results suggest that in a primate adapted for extreme psychosocial regulation of reproduction, (1) pituitary LH release is not a reliable temporal biomarker for hypothalamic GnRH release and (2) mechanisms underlying social modulation o f fertility may be mediated at the pituitary level. FUTURE DIRECTIONS We plan to investigate specific neuroendocrine alteration of pituitary gonadotropic response to hypothalamic GnRH release in subordinate female marmosets in order to increase our understanding of this potentially novel regulation of female reproductive function. KEY WORDS gonadotropin-releasing hormone, infertility, pituitary, luteinizing hormone, marmoset FUNDING NIH RR0167, NIH MH11417